Stress compensated (“SC”) cut quartz crystals have been extensively used as the resonating element in oscillator circuits as a reliable element to generate accurate frequencies. Under static conditions, i.e., an acceleration-free (vibration-free) environment, a well-designed SC-cut quartz crystal oscillator when powered will produce an output signal at a particular carrier frequency with relatively low sideband frequencies with respect to the carrier frequency. However, when the same oscillator is subjected to acceleration or to changes in spatial orientation, undesirable spurious sidebands occur in the output signal. Depending on the particular application of the oscillator, these spurious sidebands, as well as unwanted signal noise, can translate into overall system errors when motion and vibration are encountered. The effects on a quartz crystal resonating element of both periodic and random acceleration (vibration) have been well documented. However, known methods for compensating for the acceleration effects have not resulted in a sufficiently compensated crystal that can be produced with good commercial yields with economies of manufacturing.
In addition, oscillators may be subject to changes in spatial orientation, i.e., the oscillator may be mounted in a vertical position inside an instrument that is positioned on a non-vibrating platform such as a laboratory worktable. The instrument may be moved and turned 90 degrees on its side resulting in the oscillator changing its spatial orientation or positioning by 90 degrees and, thus, resulting in degradation to the oscillator's output signal. Better techniques and methods to adequately compensate for changes in spatial orientation are needed. Specifically, an apparatus and methodology is needed that seamlessly compensates from 0 Hz (no vibration but changes in spatial orientation) to 2000 Hz (with sinusoidal and/or random vibration and high g-levels). It is believed that no previously known method has ever economically compensated for both the effects of changes in oscillator spatial orientation, i.e., 0 Hz, and for higher vibration frequencies.
What has been needed and heretofore unavailable is a quartz crystal resonating element that both can effectively compensate for a broad range of conditions, such as changes in oscillator spatial orientation and periodic and random vibration effects, and a method for fabricating the oscillator that is highly reproducible and permits high yields at an optimum manufacturing cost. The present invention satisfies these needs.